To accurately form and position false teeth or caps, a dentist normally makes a negative impression of the affected tooth or teeth. The negative impression may be partial, unilateral or bilateral, depending upon the extent of work to be done; the negative impression serves as a mold for developing a die of the patient's tooth or teeth. The negative impression is obtained by partially filling a tray with thermoplastic material. The filled tray is inserted within the patient's mouth such that the teeth and adjacent gum sink into and create a cavity within the thermoplastic material. Shortly thereafter, the thermoplastic material will cure and retain an exact impression of the patient's teeth and adjacent gum. This is an essentially standard technique presently used by most dentists.
To form a tooth die, a pourable casting stone, known as pink stone is poured into the negative impression up to at least the margin or base of the tooth. The pink stone is compacted to preclude voids and remove any air bubbles. After the pink stone is at least partially cured, wax or similar lubricant is swathed upon the surface of the pink stone.
In the prior art, the base for the dental mold is made by one of two methods. First, additional pourable hardenable stone, generally referred to as yellow stone, is poured within the negative impression to cover the pink stone and the retainer with sufficient depth of yellow stone to form a solid base. After both the pink stone and the yellow stone have hardened, the tray and supported thermoplastic material is peeled away to leave a conventional dental model. Alternatively, a patty of yellow stone is formed upon a glass or other smooth surface. The partially or completely cured pink stone is placed thereupon.
In either method, pins are lodged or fixated in the pink stone to extend into and slidably engage the yellow stone. Usually, three pins per model tooth to be worked on are used. The pins serve the function of maintaining registration of the model tooth with respect to the remaining die.
Either of the prior art methods for making the base of yellow stone requires substantial technician time to manually form the yellow stone into an initial shape. After it is cured, further time is required for cutting and grinding away excess yellow stone material. The time spent and material wasted necessarily adds to the cost of the dental model to the ultimate detriment of the patient.
Either of the above processes for making the bases of dental models tends to result in each base being somewhat unique and individualized. When the dental models are placed upon a dental articulator to perform work on the dental model, a substantial amount of time and expertise is necessary to properly attach and align the upper and lower coacting dental models to reproduce the relationship of the patient's jaws. The requisite time for aligning the dental models is exacerbated by the nonuniformity of the dental model base configurations and thicknesses and requires yet further time and effort to positionally orient and attach each base upon its respective arm of the articulator.
The dental base described and illustrated in U.S. Pat. No. 4,378,929 is formed by pouring the yellow stone into a mold. The mold standardizes the width, breath, height and configuration of the base. Such standardization permits the use of indexing means in the bases to mount opposing bases of a dental model upon an articulator. Additionally, there is described and illustrated the use of an overhang for forcing a depression in the surface of the base to which the tooth die is attached, which depression delineates a platform. The tooth die (pink stone) is attached upon the platform. To sever a model tooth from the tooth die, mesial and distal saw cuts are made through the tooth die to a point just below the line of demarcation between the tooth die and the base. The line of demarcation is coincident with the surface of the platform. As the saw blade need not be angled to have the saw end clear the opposing quadrant of the tooth die, the depth of cut into the base may be minimized at a point just below the platform surface.
In U.S. Pat. No. 4,382,787, there is described an articulator attachable to opposed pairs of dental model bases through a mounting means. The articulator is particularly easily usable with size standardized bases for dental models of the type described in U.S. Pat. No. 4,378,929. One embodiment of the mounting means usable as part of the articulator includes a tab, tang or ridge for penetrable engagement with a slot formed in the rear sidewall of a dental model base.